Image forming apparatus

ABSTRACT

An image forming apparatus including a control section which detects an offset of a recording sheet being conveyed, the offset being in a main scanning direction perpendicular to a conveyance direction of the recording sheet; performs an offset regulation control which adjusts a main scanning direction image area signal in accordance with the offset; and forms a patch at a non-transfer area on an image carrier, wherein the control section performs a first control based on the offset of the recording sheet for the offset regulation control while a sub scanning direction image area signal is active for image forming on the recording sheet, and performs a second control for the offset regulation control while the image area signal in the sub scanning direction is inactive.

REFERENCE TO RELATED APPLICATION

This is divisional of application Ser. No. 12/632,346, filed Dec. 7,2009, and is also based on and claims priority under 35 U.S.C. §119 toJapanese Patent Application No. 2008-314266 filed on Dec. 10, 2008 atthe Japanese Patent Office, the entirety of all of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of Technology

The present invention relates to an image forming apparatus such as aphotocopier and printer, particularly to an image forming apparatus thatuses a sensor to detect the patch density formed on a recording sheetand to control the image forming conditions, and provides offsetregulation control of shifting an image formation area in response tothe offset during conveyance of the recording sheet.

2. Description of Related Art

One of the conventional apparatuses includes an image forming apparatusthat forms an image by the steps of:

forming an electrostatic latent image on an image carrier in conformityto image data;

generating a developed image (toner image) by developing theelectrostatic latent image using developer (toner);

transferring the generated toner image from the image carrier to arecording sheet (recording sheet) by the transfer current from atransfer device;

separating the recording sheet from the image carrier by the separationcurrent from a separation device; and

using heat and pressure to fix the recording sheet carrying the tonerimage.

In such an image forming apparatus, an image of approximate density isobtained by controlling various forms of parameters under the imageforming conditions. One of image forming conditions is the transfercondition. To be more specific, the transfer current is supplied to theimage carrier and recording sheet from a transfer device and the tonerimage is transferred to the recording sheet. The percentage of the tonertransferred to the recording sheet varies according to the value of thetransfer current. The transfer efficiency is also known to vary inconformity to the size, thickness and material of the recording sheet,temperature, humidity, the amount of charge of toner on a photoreceptor,the amount of deposited toner, the contamination of the transfer device,the amount of water contained in the recording sheet, the degree ofadhesion between the recording sheet and photoreceptor, the rotatingspeed of the photoreceptor, recording sheet conveyance speed and otherfactors. These various conditions must be taken into account beforemaking adjustments. However, it is difficult to make adjustments toensure the optimum transfer current value.

Thus, Japanese Unexamined Patent Application Publication No. H5-241390to be described below discloses the technique wherein the toner image(patch) in conformity to the image data of a predetermined density isformed on the recording sheet, the density of the toner image on therecording sheet is measured, and the transfer current is corrected inconformity to the difference between the density estimated from theimage data and the actually measured density.

For such a patch, the patch on the image carrier is read by a sensorusing the non-transfer area on the image carrier, i.e., the spacebetween the images to be transferred in the process of image formation,whereby the real-time implementation is possible in the process of imageformation. This arrangement improves productivity without having tosuspend linage production. This type of technique is also disclosed inthe Japanese Unexamined Patent Application Publication No. 2005-289035.

Further, the Japanese Unexamined Patent Application Publication No.2007-316237 discloses the technique of automatically detecting theposition for forming the above-mentioned patch and correcting theposition for forming the patch.

Another apparatus in the conventional art is an image forming apparatusthat provides offset regulation control in such a way that the offset inthe direction perpendicular to the direction of the recording sheetbeing conveyed (the main scanning direction) is detected duringrecording sheet conveyance, and the image formation area on the imagecarrier is shifted in response to the offset. Thus, even if therecording sheet is conveyed by such an offset regulation control withthe recording sheet being offset in the conveyance mode, an image willbe transferred at a desired position.

Starting from the leading-edge of the image formation area for therecording sheet when an offset has occurred, the offset regulationcontrol is performed continuously up to the leading edge of the imageformation area of the recording sheet where a different offset hasoccurred, including the non-image formation area.

Still another apparatus in the conventional art is an image formingapparatus wherein, as described above, various forms of predeterminedpatches such as a density patch or registration mark are formed on thenon-image area of the image carrier, and various forms of patches onthis image carrier are read by a sensor, whereby the above-mentionedimage forming conditions are controlled.

The inventors of the present application have found out in theabove-mentioned case that, when the patch forming position is changed tothe direction of main scanning by the aforementioned offset regulationcontrol, the patch on the image carrier cannot be detected by the sensorif the patch is formed in finer patterns.

For example, in FIGS. 8 and 9, both the transfer area and thenon-transfer area including the patch before the next transfer areastarts are shifted to the right of the drawings by the offset regulationcontrol on the Nth page.

In a similar manner, in FIGS. 8 and 9, both the transfer area and thenon-transfer area including the patch are shifted to the left of thedrawings by the offset regulation control on N+1th page until the nexttransfer area starts.

To put it another way, in FIG. 9, the transfer area and the non-transferarea immediately thereafter are in the same direction indicated by thebroken line. This suggests that the same offset regulation control isperformed in the transfer area and the non-transfer area immediatelythereafter.

Since the shift in the transfer area agrees with the offset of therecording sheet, the relative misalignment is cancelled. Thus, an imagefree of misalignment is formed on the recording sheet. In the meantime,if the patch on the image carrier in the non-transfer area is shifted,positional misalignment occurs with respect to the sensor at the fixedposition. This leads to the inability of reading a patch.

In view of the problems described above, it is an object of the presentinvention to provide an image forming apparatus capable of ensuringcompatibility between the control of image forming conditions using apatch and offset regulation control conforming to the recording sheetoffset.

SUMMARY OF THE INVENTION

One aspect of the present invention is an image forming apparatuscomprising a control section which detects an offset of a recordingsheet being conveyed, the offset being in a main scanning directionperpendicular to a conveyance direction of the recording sheet; performsan offset regulation control which adjusts a main scanning directionimage area signal which represents an image area in the main scanningdirection in accordance with the offset; forms a patch at a non-transferarea where image to be transferred to the recording sheet is not formedon an image carrier; and controls an image forming condition by readingthe patch by a sensor, wherein the control section performs a firstcontrol based on the offset of the recording sheet for the offsetregulation control while a sub scanning direction image area signalwhich represents an image area in a sub scanning direction perpendicularto the main scanning direction is active for image forming on therecording sheet, and performs a second control for the offset regulationcontrol while the sub scanning direction image area signal is inactive.

Another aspect of the present invention is an image forming apparatuscomprising a control section which detects an offset of a recordingsheet being conveyed in a main scanning direction perpendicular to aconveyance direction of the recording sheet; performs an offsetregulation control which adjusts a main scanning direction image areasignal which represents an image area in the main scanning direction inaccordance with the offset; forms a patch at a non-transfer area whereimage to be transferred to the recording sheet is not formed on an imagecarrier; and controls an image forming condition by reading the patch bya sensor, wherein the control section performs a first control based onthe offset of the recording sheet for the offset regulation control atan image transferring area where image is transferred to the imagerecording sheet, and performs a second control for the offset regulationcontrol at the non-transfer area.

Another aspect of the present invention is an An image forming apparatuscomprising a control section which detects an offset of a recordingsheet being conveyed in a main scanning direction perpendicular to aconveyance direction of the recording sheet; performs an offsetregulation control which adjusts a main scanning direction image areasignal which represents an image area in the main scanning direction inaccordance with the offset; forms a patch at a non-transfer area whereimage to be transferred to the recording sheet is not formed on an imagecarrier; and controls an image forming condition by reading the patch bya sensor, wherein the control section performs a first control based onthe offset of the recording sheet for the offset regulation controlwhile a sub scanning direction image area signal which represents animage area in a sub scanning direction perpendicular to the mainscanning direction is active for image forming on the recording sheet,and performs a second control for the offset regulation control while apatch area signal which represents a patch forming area is active at thenon-transfer area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 2 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 3 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 4 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 5 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 6 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 7 is a schematic diagram representing the configuration of theimage forming apparatus as an embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the conventional operations.

FIG. 9 is an explanatory diagram showing the conventional operations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the following describes the preferred form ofan embodiment for the implementation of the present invention:

[Configuration of First Embodiment 1]

The following describes the configuration of the image forming apparatus100 as the first embodiment with reference to FIG. 1 (block diagram).

The following does not include the description of the general portionsof the already known image forming apparatus which are not directlyrelated to the operation or control characteristic of the presentembodiment.

It should be noted that, in the present embodiment, the sub-scanningdirection is defined as the direction wherein an image carrier is movedand a recording sheet is conveyed, and the main scanning direction isdefined as the direction perpendicular to the sub-scanning direction.The recording sheet is conveyed in the sub-scanning direction and theimage carrier is moved in the sub-scanning direction. Concurrently withthis process, a two-dimensional image is formed by exposure on the imagecarrier in the main scanning direction, and the image on the imagecarrier is transferred onto the recording sheet, whereby a desired imageis formed on the recording sheet.

In the image forming apparatus 100, the control section 101 is composedof a CPU and others in order to control various portions of the imageforming apparatus 100. The control section 101 at least implements:

the control of forming a patch in the non-transfer area on the imagecarrier, reading the patch by a sensor, and adjusting the image formingconditions;

the offset regulation control of detecting the offset of the conveyedrecording sheet in the main scanning direction and regulating the imagearea signal in the main scanning direction; and

the control of ensuring compatibility between the image formingconditions control and offset regulation control.

An operation section 103 is used for various forms of operation inputsby the operator of the image forming apparatus, and is provided withvarious switches and keys.

A storage section 105 is a storage device for storing various forms ofdata. In this embodiment, the storage section 105 stores the density andpattern of the patch used in the control of image conditions, patchformation position, and various forms of data for control.

The image area signal generation section 110 includes the sub-scanningdirection image area signal generation section 111 for generating asub-scanning direction image area signal (V-Valid) that shows thesub-scanning direction in the image formation area on the image carrier;and the main scanning direction image area signal generation section 112for generating the main scanning direction image area signal (H-Valid)showing the main scanning direction in the image formation area on theimage carrier.

In this embodiment, the area on the image carrier, wherein both the mainscanning direction image area signal and sub-scanning direction imagearea signal are active, indicates the “transfer area”, wherein an imageis transferred onto the recording sheet. That is, the “transfer area” isan area where image to be transferred to the image recording sheet isformed on the image carrier.

Further, in this embodiment, the area on the image carrier wherein atleast one of the main scanning direction image area signal andsub-scanning direction linage area signal is inactive indicates the“non-transfer area ” wherein an image is not transferred onto therecording sheet. That is, the “non-transfer area” is an area where imageto be transferred to the image recording sheet is not formed on theimage carrier.

The patch generation section 120 is a patch image generation device forgenerating the images of various forms of patches in the non-transferarea of the image carrier. In this embodiment, the patch generationsection 120 includes:

a density patch generation section 121 for generating the density patchfor density adjustments;

a registration patch generation section 122 for generating theregistration patch for registration adjustments; and

a toner band generation section 123 for generating a toner band patch.

An image processing section 130 performs image processing wherein theimage data for forming an image is converted into the form suitable forimage formation.

A synthesizing section 140 is a data synthesizing section that receivesthe patch image from the patch generation section 120 and image datafrom the image processing section 130, and supplies the same to theprint engine 100P.

Referring to FIG. 2, the following describes the configuration of theprint engine 100P. The sheet supply section 150 is a sheet supply devicefor ensuring that the recording sheets placed on a plurality of sheetsupply trays 150T are fed to the image formation position by a sheetsupply roller.

The conveyance section 160 is a conveyance device for ensuring that therecording sheet fed out of the sheet supply section 150 is conveyed at apredetermined conveyance speed, and includes a registration roller,various forms of other conveyance rollers and a conveyance belt.

To detect the misalignment of the recording sheet fed out of the sheetsupply section 150 in the main scanning direction, the offset sensors160 s 1 composed of the line sensors wherein the main scanning directionis the same as the longitudinal direction are arranged at the outlet ofthe sheet supply section 150 and the succeeding positions. Further, theconveyance sensors 160 s 2 such as leading-edge detection sensors fordetecting the leading edge of a recording sheet are arranged atpredetermined positions of various parts of the conveyance section 160.

The process unit 170 is a device for performing various forms ofoperations to form an image on the recording sheet, and includes acharging section 171 for charging the photoreceptor as specified, anexposure section 172 for exposing a photoreceptor in response to theimage data, a photoreceptor 173 as an image carrier wherein anelectrostatic latent image is formed by exposure, a development section174 for developing the electrostatic latent image of the photoreceptor173 and converting it into a toner image, an intermediate transfermember 175 as an image carrier wherein the toner image on thephotoreceptor 173 is transferred and the image is carried thereby, and atransfer section 176 provided with a transfer roller 176 a and atransfer roller 176 b.

When the image forming apparatus is a color image forming apparatuswherein toner images of multiple colors are synthesized, the chargingsection 171, exposure section 172, photoreceptor 173, and developmentsection 174 are provided for each color in the process unit 170, asshown in FIG. 2. Thus, the toner images of different colors aresuperimposed on the intermediate transfer member 175, and aretransferred on the recording sheet in the final step.

The photoreceptors 173Y, 173M, 173C and 173K as image carriers areprovided with sensors 170sY, 173sM, 173sC and 173sK for detecting thepatch formed in the non-transfer area, respectively. It is also possibleto arrange such a configuration that patches are detected on theintermediate transfer member 175, although the photoreceptors areprovided with sensors in this example.

While sandwiching and conveying the recording sheet with the toner imagetransferred thereon, the fixing section 180 uses heat and pressure toperform a fixing operation to ensure that the toner image is fixed ontothe recording sheet.

[Operation of the First Embodiment]

Referring to the explanatory diagrams of FIGS. 3 and 4, the followingdescribes the operations of the image forming apparatus in the firstembodiment.

In the first embodiment, the control section 101 performs the offsetregulation control to regulate the main scanning direction image areasignal, when the offset sensor 160 s 1 has detected the offset of therecording sheet in the main scanning direction conveyed by theconveyance section 160. In this case, the main scanning direction imagearea signal generation section 112 which has received the instruction ofperforming the offset regulation control from the control section 101,accepts the index signal, pixel clock and the offset detection result,and generates the main scanning direction image area signal H-Valid inconformity to the offset during the conveyance of the recording sheet.In FIG. 3, the portion wherein the H-Valid is active is indicated byhatching. This ensures an image is formed (transferred) on the recordingsheet without being affected by the offset at the time of conveyance.

Further, upon receipt of the instruction of generating a density patchfor density adjustment, a registration patch for registration adjustmentand a toner band patch from the control section 101 in the non-transferarea during the image formation process, the patch generation section120 forms a patch in the non-transfer area on the photoreceptor 173.Then the patch is read by the sensor 170 s. Based on the result havingbeen obtained, the control section 101 controls the image formingconditions.

In FIG. 3, the portion wherein the V-Valid is active is indicated byhatching. To be more specific, offset regulation control is performed asusual in the transfer area wherein the V-Valid is active, whereas theoffset regulation control is not performed in the non-transfer areawherein the V-Valid is inactive.

This ensures that the offset regulation control is performed only whenthe image is formed in the transfer area, and eliminates the possibilityof the patch position being changed with offset regulation control. FIG.4 uses the hatching of oblique lines to denote the transfer area whereinthe offset regulation control is performed, and uses the hatching ofhorizontal lines to indicate the area around the patch (non-transferpatch area) which is the non-transfer area in a state where the offsetregulation control is not performed.

In this case, the main scanning direction image area signal generationsection 112 generates the main scanning direction image area signalH-Valid that causes the offset regulation control to be performed if theV-Valid is active. Further, the main scanning direction image areasignal generation section 112 generates the main scanning directionimage area signal H-Valid that does not cause the offset regulationcontrol to be performed if the V-Valid is inactive.

In this case, the main scanning direction image area signal generationsection 112 can be configured in such a way that, when the H-Valid isgenerated and outputted, the value of the register (not illustrated) inthe image area signal generation section 112 is outputted after havingbeen rewritten by software (software processing).

Alternatively, in this case, the main scanning direction image areasignal generation section 112 can be configured in such a way that, whenthe H-Valid is generated and outputted, the value of the register (notillustrated) in the image area signal generation section 112 isoutputted after having been rewritten by replacing the value stored inanother register or storage section 105 (hardware processing).

This arrangement ensures compatibility between the control of the imageforming conditions using a patch and offset regulation controlconforming to the offset of the recording sheet.

[Second Embodiment]

The following describes the operation of the image forming apparatus ofthe second embodiment.

In the second embodiment as well, similarly to the case of the firstembodiment, the control section 101 performs the offset regulationcontrol to regulate the main scanning direction image area signal, whenthe offset sensors 160 s 1 has detected the offset of the recordingsheet in the main scanning direction conveyed by the conveyance section160. In this case, having received the instruction of executing theoffset regulation control from the control section 101, the mainscanning direction image area signal generation section 112 accepts theindex signal, pixel clock and offset detection result, and generates themain scanning direction image area signal H-Valid in conformity to theoffset during the conveyance of the recording sheet. In FIG. 5, theportion wherein the H-Valid is active is indicated by hatching. Thisensures an linage is formed (transferred) on the recording sheet withoutbeing affected by the offset at the time of conveyance.

Further, upon receipt of the instruction of generating a density patchfor density adjustment, a registration patch for registration adjustmentand a toner band patch from the control section 101 in the non-transferarea during the image formation process, the patch generation section120 forms a patch in the non-transfer area on the photoreceptor 173.Then the patch is read by the sensor 170 s. Based on the result havingbeen obtained, the control section 101 controls the image formingconditions.

In FIG. 5, the portion wherein the V-Valid is active is indicated byhatching. To be more specific, offset regulation control is performed asusual in the transfer area wherein the V-Valid is active.

In the non-transfer area wherein the V-value is inactive, the offsetregulation control is performed according to a predetermined fixedvalue. The fixed value in this case can be the value corresponding tothe state wherein the offset regulation control is not performed, or thevalue for forming the optimum patch.

This ensures that, except when an image is being formed in the transferarea, the offset regulation control is performed according to the valuedifferent from the offset detection result, and therefore, eliminatesthe possibility of the patch position being changed with offsetregulation control.

In this case, the main scanning direction image area signal generationsection 112 generates the main scanning direction image area signalH-Valid that causes the offset regulation control to be performed if theV-Valid is active. Further, the main scanning direction image areasignal generation section 112 generates the main scanning directionimage area signal H-Valid that does not cause the offset regulationcontrol to be performed if the V-Valid is inactive.

In this case, the main scanning direction image area signal generationsection 112 can be configured in such a way that, when the H-Valid isgenerated and outputted, the value of the register (not illustrated) inthe image area signal generation section 112 is outputted after havingbeen rewritten by software (software processing).

Alternatively, in this case, the main scanning direction image areasignal generation section 112 can be configured in such a way that, whenthe H-Valid is generated and outputted, the value of the register (notillustrated) in the image area signal generation section 112 isoutputted after having been rewritten by replacing the value with avalue stored in another register or storage section 105 (hardwareprocessing).

This arrangement ensures compatibility between the control of the imageforming conditions using a patch and offset regulation controlconforming to the offset of the recording sheet.

[Third Embodiment]

The following describes the operation of the image forming apparatus ofthe third embodiment.

In the third embodiment, the sub-scanning direction image area signalgeneration section 111 includes the sub-scanning direction image areasignal generation section 111 a for generating the regular sub-scanningdirection image area signal V-Valid, and the sub-scanning directionimage area signal generation section 111 b for a patch that generatesthe sub-scanning direction image area signal V-Valid′ for a patch, asbefore, as shown in the block diagram of FIG. 6. The sub-scanningdirection image area signal generation section 111 of FIG. 1 canincorporate a similar structure.

In the third embodiment as well, similarly to the case of the first andsecond embodiments, the control section 101 performs the offsetregulation control to regulate the main scanning direction image areasignal, when the offset sensor 160 s 1 has detected the offset of therecording sheet in the main scanning direction conveyed by theconveyance section 160. In this case, having received the instruction ofexecuting the offset regulation control from the control section 101,the main seaming direction image area signal generation section 112accepts the index signal, pixel clock and offset detection result, andgenerates the main scanning direction image area signal H-Valid inconformity to the offset during the conveyance of the recording sheet.

In FIG. 7, the portion wherein the H-Valid is active is indicated byhatching. This ensures an image is formed (transferred) on the recordingsheet without being affected by the offset at the time of conveyance.

Further, upon receipt of the instruction of generating a density patchfor density adjustment, a registration patch for registration adjustmentand a toner band patch from the control section 101 in the non-transferarea during the image formation process, the patch generation section120 forms a patch in the non-transfer area on the photoreceptor 173 whenthe sub-scanning direction image area signal V-Valid′ for pitch isactive. Then the patch is read by the sensor 170 s. Based on the resulthaving been obtained, the control section 101 controls the image formingconditions.

In FIG. 7, the portion wherein the V-Valid and V-Valid′ are active isindicated by hatching. To be more specific, the offset regulationcontrol is performed as usual in the transfer area wherein the V-Validis active.

In the non-transfer area wherein the v-Valid′ is active, the offsetregulation control is not performed or is performed according to apredetermined fixed value. The fixed value in this case can be the valuecorresponding to the state wherein the offset regulation control is notperformed, or the value for forming the optimum patch.

This ensures that, except when an image is being formed in the transferarea, offset regulation control is performed according to the valuedifferent from the offset detection result based on the sub-scanningdirection image area signal V-Valid′ for patches, and therefore,eliminates the possibility of the patch position being changed withoffset regulation control.

In this case, the main scanning direction image area signal generationsection 112 can be designed in such a way that, when the H-Valid isgenerated and outputted, the value of the register (not illustrated) inthe image area signal generation section 112 is outputted after havingbeen rewritten by software (software processing).

Alternatively, in this case, the main scanning direction image areasignal generation section 112 can be designed in such a way that, whenthe H-Valid is generated and outputted, the value of the register (notillustrated) in the image area signal generation section 112 isoutputted after having been rewritten by software (software processing)by replacing the value with a value stored in another register orstorage section 105 (hardware processing).

This arrangement ensures compatibility between the control of the imageforming conditions using a patch and offset regulation controlconforming to the offset of the recording sheet.

[Embodiment 4]

In the aforementioned third embodiment, only one type of thesub-scanning direction image area signal V-Valid′ for a patch was shown.In the presence of a plurality of patches such as a density patch,registration patch and toner band, density control or registrationcontrol can be performed in such a way that the sub-scanning directionimage area signals V-Valid′ (V-Valid′, Valid″, . . . ) for patches areprepared to conform to these patches, and the patches are formedaccording to these signals, respectively, without being affected byoffset regulation control (or offset regulation control using a fixedvalue).

The aforementioned procedure can be performed when the sub-scanningdirection image area, signals V-Valid′ for various forms of patches areoverlapped. Even if overlap occurs in the sub-scanning direction, noproblem arises since patches formed in the non-transfer area arepositioned differently in the main scanning direction.

According to the present embodiment, the following advantages areobtained.

1. Except when an image is being formed in the transfer area, the offsetregulation control is not performed. This eliminates the possibility ofthe patch position being changed with offset regulation control, andtherefore, ensures compatibility between the control of the imageforming conditions using a patch and offset regulation controlconforming to the offset of the recording sheet.

2. Except when an image is being formed in the transfer area, the offsetregulation control is performed with the amount of regulation differentfrom that in the transfer area. This eliminates the possibility of thepatch position being changed with offset regulation control, andtherefore, ensures compatibility between the control of the imageforming conditions using a patch and offset regulation controlconforming to the offset of the recording sheet.

3. Means are provided to eliminate the possibility of the patch positionbeing changed with offset regulation control on the regular recordingsheet in the transfer area, and therefore, to ensure compatibilitybetween the control of the image forming conditions using a patch andoffset regulation control conforming to the offset of the recordingsheet.

4. Means are provided to eliminate the possibility of the patch positionbeing changed with offset regulation control on the regular recordingsheet in the transfer area, and therefore, to ensure compatibilitybetween the control of the image forming conditions using a patch andoffset regulation control conforming to the offset of the recordingsheet.

5. Means are provided to eliminate the possibility of the patch positionbeing changed with offset regulation control on the regular recordingsheet in the transfer area, and to ensure adequate adjustments are madeaccording to the type of the patch; hence, to ensure compatibilitybetween the control of the image forming conditions using a patch andoffset regulation control conforming to the offset of the recordingsheet.

What is claimed is:
 1. An image forming apparatus comprising a controlsection which detects an offset of a recording sheet being conveyed in amain scanning direction perpendicular to a conveyance direction of therecording sheet; performs an offset regulation control which adjusts amain scanning direction image area signal which represents an image areain the main scanning direction in accordance with the offset; forms apatch at a non-transfer area where image to be transferred to therecording sheet is not formed on an image carrier; and controls an imageforming condition by reading the patch by a sensor, wherein the controlsection performs a first control which generates a main scanningdirection image area signal for adjusting the offset of the recordingsheet at an image transferring area where image is transferred to theimage recording sheet while a sub scanning direction image area signalwhich represents an image area in a sub scanning direction perpendicularto the main scanning direction is active and forms the image to betransferred to the recording sheet at the image transferring area on theimage carrier in accordance with the adjusted main scanning directionimage area signal, and performs a second control which generates a mainscanning direction image area signal for performing the offsetregulation control according to a fixed value and forms the patch at anon-transfer area on the image carrier in accordance with the adjustedmain scanning direction image area signal at the non-transfer area whilesub scanning direction image area signal is inactive.
 2. The imageforming apparatus of claim 1, wherein the patch comprises at least oneof a density patch for density adjustments, a registration patch forregistration adjustments, and a toner band patch.
 3. The image formingapparatus of claim 1, wherein the control section performs the secondcontrol which generates the main scanning direction image area signalfor performing the offset regulation according to the fixed value andforms the patch at the non-transfer area on the image carrier inaccordance with the adjusted main scanning direction image area signalwhile a patch area signal which represents a patch forming area isactive at the non-transfer area.
 4. The image forming apparatus of claim3, wherein the fixed value is a fixed value in accordance with a type ofthe patch and the control section performs the second control whichgenerates the main scanning direction image area signal for performingthe offset regulation according to the fixed value and forms the patchat the non-transfer area on the image carrier in accordance with theadjusted main scanning direction image area signal.
 5. The image formingapparatus of claim 3, wherein the patch comprises at least one of adensity patch for density adjustments, a registration patch forregistration adjustments and a toner band patch.
 6. The image formingapparatus of claim 1, wherein the patch is formed at the none-transferarea between the image formed at the transfer area and a subsequentimage to be formed subsequently at the transfer area on the imagecarrier.
 7. The image forming apparatus of claim 4, wherein the type ofpatch comprises at least two of a density patch for density adjustments,a registration patch for registration adjustments, and a toner brandpatch.